The field of the invention is automatic gain control (AGC) circuits employed in microwave frequency applications.
The function of an AGC circuit is to maintain a constant output level in the presence of varying input levels. Conventional AGC circuits typically employ feedback techniques. Compensation circuits or bandwidth limitations are used to maintain loop stability in the presence of parasitic reactances, resulting in reducing the settling speed of the AGC circuit.
An AGC circuit is described in "A 2 to 8 GHz Leveling Loop Using a GaAs MMIC Active Splitter and Attenuator," Gary S. Barta et al, 1986 Microwave and Millimeter Wave Monolithic Circuits Symposium, pages 75-79. The circuit described used an op-amp feedback loop to provide the proper voltages to a GaAs FET attenuator.
An object of the present invention is to provide a microwave signal automatic gain circuit characterized by fast settling times.
A further object is to provide a microwave signal automatic gain circuit operable over a relatively wide bandwidth and which provides a constant characteristic impedance.